Chinese alchemy has a history of more than two thousand years. It is divided into two main branches, known as Waidan 外丹, or External Alchemy, and Neidan 內丹, or Internal Alchemy. Waidan (literally, “external elixir”) arose by the 2nd century bce; it is based on compounding elixirs through the manipulation of natural substances—primarily minerals and metals—which release their essences when they are submitted to the action of fire. Neidan (literally, “internal elixir”), documented from the 8th century ce, aims instead to produce the elixir within the person itself, according to two main models of doctrine and practice: by causing the primary components of the cosmos and the human being—essence (jing精), breath (qi氣), and spirit (shen神)—to revert to their original states; or by purifying the mind from defilements and passions, in order to “see one’s Nature” (jianxing見性). Neither alchemy as a whole, nor Waidan or Neidan individually, constitute “schools” of Daoism, with a definite canonical corpus and a single line of transmission. On the contrary, the respective sources display wide differences in both doctrines and practices. However, if one may attempt to formulate a broad statement that encompasses at least a large part of its different forms, Chinese alchemy is characterized by a foundation in doctrinal principles concerning the relation between the Dao 道 (Way) and the world. The cosmos as we know it is deemed to be the last stage in a sequence of “transformations” leading from Non-Being (wu無) to Unity (yi一), duality (Yin and Yang 陰陽), and finally multiplicity (wanwu萬物, “ten thousand things”). Alchemists intend to trace this sequence backwards and return to its inception. In both Waidan and Neidan, the practice is variously said to grant transcendence (a state described by such expressions as “joining with the Dao,” hedao合道), “immortality” (mainly meant as a spiritual condition), longevity, healing (either in a broad sense or with regard to specific illnesses), and—especially in Waidan—communication with the deities of the celestial pantheon and protection from spirits, demons, and other malevolent entities.